A serial bus system is known from IEEE standard 1394 [1], in which a plurality of terminals (nodes) are connected either via a 4-6-strand cable or an optical fiber. At least one node may be designed so that it is able to assume additional administrative functions for the network (bus management).
In addition to the above standard, there is the bus-independent expansion specification known as HAVi (Home Audio Video interoperability) [2]. The HAVi specification describes remote control of devices using a resource manager which seizes a resource (device) on request and also releases it again.
The HAVi specification describes a distributed model in which devices are controlled by control modules, also known as device control modules (DCM). DCMs run as software elements on the device which is to perform control functions on another device. A DCM is specific for a certain device or a class of devices.
The HAVi standard offers the possibility of allocating two different security levels to one software element. A software element is classified as “trusted” if it has been adequately tested by the manufacturer. In the case of software elements which must be dynamically loaded into the system, the authenticity of the software element must be verified by a digital signature. All DCMs must have a “trusted” status. Software elements designated as “untrusted” are all of those not marked as “trusted” by the manufacturer. On the basis of this classification, the recipient of a request decides whether to trust the sending software element, i.e., even an “untrusted” software element may send requests, but it is not certain whether its request will be met.